In metalworking operations where a workpiece is machined, equipment of some type is necessary to hold the workpiece in position in a machine tool so the machining process can be successfully carried out. This type of equipment is known as "workholding" equipment. In the production of toothed articles, such as gears, workholding equipment can be generally categorized as two types, chucks and arbors.
Chucks hold a workpiece by contracting a component called a "collet" around the workpiece or a component thereof. For example, when a bevel or hypoid pinion with integral shaft is placed in a chuck, it is usually the shaft that is gripped by the collet which has been reduced in diameter to grip the shaft to hold the pinion in position. Examples of chucks for gripping pinion shanks can be found in U.S. Pat. Nos. 3,083,976 to Stark and 3,244,427 to Taschl.
Arbors grip a workpiece by expanding a collet into contact with a surface of the workpiece. As an example, a bevel ring gear is placed on an arbor and the collet is expanded until contact of sufficient force is established with the surface of the bore of the ring gear to hold the ring gear in position during machining. An example of an arbor for a ring gear can be found in U.S. Pat. No. 3,735,994 to Jaehn. An arbor for expanding into contact with the bore of a pinion can be found in U.S. Pat. No. 3,517,939 to Jaehn and an expandable arbor for holding a stack of workpieces can be found in U.S. Pat. No. 4,198,066 to Deprez et al.
In either chucks or arbors, the force necessary to contract or expand the collet mechanism is usually provided by a draw rod in the machine tool. The draw bar is advanced and/or retracted usually with a hydraulically operated piston. In most instances, movement of the draw rod in the axial direction of the chuck or arbor causes opposed angled surfaces of components within the workholding equipment to slide relative to one another resulting in inward (contracting) or outward (expanding) movement of the collet to grip a workpiece or component part thereof. Generally, one angled surface is found on the collet and the other angled surface is found on an expander or actuator attached via a draw bar to the draw rod.
In addition to the hydraulic mechanism required for advancing and withdrawing the draw rod for operating the collet, many machine tools include a second hydraulic system comprising a second draw rod for securing the workholding equipment in position on the machine tool. For example, in a machine for producing cylindrical gears (spur and/or helical) by hobbing, such as shown in U.S. Pat. No. 5,228,814 to Suwijn, a first hydraulic system is utilized to advance and retract a draw rod connected to an arbor for expanding and contracting a collet within the bore of one or more workpiece blanks. In addition, a second hydraulic system may be included to advance and retract a draw rod in a clamping mechanism for securing the arbor to the hobbing machine.
In recent years there has been a movement toward cutting both bevel and cylindrical gears in the absence of cutting fluids. Such processes are known in the art as "dry" processes. A discussion of dry hobbing of cylindrical gears can be found in Phillips, "New Innovations in Hobbing--Part II", Gear Technology, November/December 1994, pp. 26-30. With dry cutting, the expense of purchasing and disposing of coolant is eliminated as is the environmental hazard associated with smoke and oil mist generated during the cutting process. Furthermore, equipment for removing smoke and mist from the machining chamber, and for separating metal chips from coolant, is no longer necessary thus reducing the cost of the particular machine.
In addition to the cost and environmental advantages of eliminating coolant from the cutting process, reducing or eliminating hydraulic liquids from machine systems (such as workholding or workpiece clamping systems) brings similar benefits. Eliminating hydraulic liquid (such as oil) from a machine system brings with it reduced costs since there is no need to purchase, or dispose of, the hydraulic liquid. Furthermore, the hazard and expense of cleaning up hydraulic liquid resulting from broken hoses is also eliminated. It can be seen that advantages exist for ridding the machine tool of some or all systems utilizing hydraulic liquids.
Possibilities that exist for eliminating hydraulic fluids in machines are replacing hydraulic liquids with air, where appropriate, and/or combining the tasks performed by two or more hydraulic systems whereby the same tasks are accomplished by fewer, preferably one, hydraulic or pneumatic system.
It is an object of the present invention to provide an apparatus for securing workholding equipment to a machine tool whereby the workholding equipment is secured by the same machine system that performs clamping of a workpiece on the workholding equipment. Thus, a second separate system for securing the workholding equipment to the machine tool is no longer necessary.